There's a guy here in town that replaced the ecm on his 1998 Silverado, and now it won't idle correctly and it misses badly.

I scanned the ecm with HPTuners, and it lists the truck as a 1998 Blazer (S10) with a V6. Then I got a tune for a stock 98 V8 silverado in the tune repository. I compared the silverado file with the s10 blazer file, and copied the settings between the two. Now the pickup starts, runs, and drives, but it shakes and misses horribly. None of the gauges work correctly. 60mph on the speedometer is more like 20mph in reality.

Is there a place to change the firing order in this tune like you can with the newer gm trucks? What is going on with the gauges? The service number between the two ecms is not the same.

What am I doing wrong? Is there more than a software difference between the two ecms?

 

It needs more than just the settings, you need the entire calibrations for a 1998 Silverado. Also, since the PCM was calibrated for a V6 and now is in a V8 it will need a complete crank relearn done to it. Don't forget to swap the knock module.

 

Can I just license a stock tune for a 1998 silverado V8 and flash it to the V6 blazer pcm? What is the story behind changing the knock module?

 

I flashed a V8 tune to the V6 ECM. The truck runs 100% better now. I also did the crank relearn on it. But I still don't have a working tach or speedometer. The needles move around some, but they read way off. A light on the instrument cluster keeps saying "check gages." Everything in the HPTuners scanner looks ok. I did verify that I had disabled VATS

What am I overlooking?

 

Just went and scanned the pickup again. The VCM Scanner shows that the speed and tach readings are where they need to be. Maybe I have a bad instrument cluster? Is that a known problem on the 96-99 pickups?